1. Field of the Invention
The present invention provides a spraying method and apparatus for spraying a starting material slurry through a nozzle in a continuous hydrothermal reaction, particularly under subcritical to supercritical conditions beyond the saturated vapor temperature to form fine particles without agglomeration thereof for efficiently effecting the hydrothermal reaction.
2. Description of the Prior Art
Since the rates of reactions of many oxides such as silica and alumina with high-pressure steam, particularly water having a temperature of at least the critical temperature, become fast in the presence of high-temperature water, particularly high-temperature and high-pressure water, hydrothermal synthesis reactions are widely carried out by making much of this phenomenon. A technique of hydrothermal synthesis of particles under pressurized conditions beyond the critical pressure (Tp=218.3 atm) in a temperature range beyond the saturated vapor temperature, particularly beyond the critical temperature (e.g., Tc=374.degree. C. for water), is carried out according to a batch method. In a large-scale batch method, however, a long heat-up time from the point of time when a starting material is set is taken together with a long temperature dropping time besides the period of time during which the desired temperature and pressure are maintained. Furthermore, there is a limit to efficient synthesis with one equipment because of batchwise production.
On the other hand, a method wherein a slurry is continuously fed through assembled piping for treatment therof is disclosed, for example, in Japanese Patent Laid-Open No. 57,112/1978, but is not aimed at a hydrothermal reaction of particles to be different in purpose from the present invention. Besides, Japanese Patent Publication No. 5,136/1990 discloses a technology according to which a reaction is effected under the saturated vapor pressure. There are no continuous hydrothermal reaction technologies according to which a hydrothermal reaction of particles is effected with such assembled pipings as to maintain a pressurized state particularly at a temperature exceeding the critical temperature, followed by temperature drop and pressure reduction, and subsequent discharge of the reacted particles.
When a hydrothermal reaction is to be consistently effected in a continuous piping, there arise various difficulties such as a problem with feeding of a starting material slurry, a problem with retention of a piping in a state of being heated at a high temperature, and a problem with withdrawal of synthesized particles. The present invention is to solve a problem involved particularly in feeding a starting material slurry into a reaction chamber. More specifically, even if a starting material slurry is flowed in a piping in a temperature range beyond the saturated vapor temperature, particularly beyond the critical temperature, the solid in the slurry may possibly be separated to be stuffed in the piping because water is in the form of steam. In view of this, according to the present invention, the solid in the slurry is finely sprayed and then fed into a reaction chamber in order to efficiently effect a reaction thereof without the sliding being stuffed in a piping.